Question

到目前为止，我所做的是

public class GalleryView extends Activity {
public Context context=getApplicationContext();

public Map< Integer,Drawable> dayMap;
Bitmap icon1 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica1);
Drawable d1 =new BitmapDrawable(context.getResources(),icon1);

Bitmap icon2 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica2);
Drawable d2 =new BitmapDrawable(context.getResources(),icon2);

Bitmap icon3 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica3);
Drawable d3 =new BitmapDrawable(context.getResources(),icon3);

Bitmap icon4 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica4);
Drawable d4 =new BitmapDrawable(context.getResources(),icon4);

Bitmap icon5 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica5);
Drawable d5 =new BitmapDrawable(context.getResources(),icon5);

ImageView imageView;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main_gallery);
    dayMap=new HashMap<Integer,Drawable>();
    dayMap.put(0,d1);
    dayMap.put(1,d2);
    dayMap.put(2,d3);
    dayMap.put(3,d4);
    dayMap.put(4,d5);

    Gallery ga = (Gallery)findViewById(R.id.Gallery01);
    ga.setAdapter(new ImageAdapter(context));

    imageView = (ImageView)findViewById(R.id.ImageView01);
    ga.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
                long arg3) {
            Toast.makeText(getBaseContext(), 
                    "You have selected picture " + (arg2+1) + " of Antartica", 
                    Toast.LENGTH_SHORT).show();
            imageView.setImageDrawable(dayMap.get(arg2));

        }

    });

}


public class ImageAdapter extends BaseAdapter {

    private Context ctx;
    int imageBackground;

    public ImageAdapter(Context c) {
        ctx = c;
        TypedArray ta = obtainStyledAttributes(R.styleable.Gallery1);
        imageBackground = ta.getResourceId(R.styleable.Gallery1_android_galleryItemBackground, 1);
        ta.recycle();
    }

    @Override
    public int getCount() {

        return dayMap.size();
    }

    @Override
    public Object getItem(int arg0) {

        return arg0;
    }

    @Override
    public long getItemId(int arg0) {

        return arg0;
    }

    @Override
    public View getView(int arg0, View arg1, ViewGroup arg2) {
        ImageView iv = new ImageView(ctx);
        iv.setImageDrawable(dayMap.get(arg0));
        iv.setScaleType(ImageView.ScaleType.FIT_XY);
        iv.setLayoutParams(new Gallery.LayoutParams(160,130));
        iv.setBackgroundResource(imageBackground);
        return iv;
    }

}

}

但是我收到了这个错误 -

06-26 17:29:27.171: E/AndroidRuntime(853): FATAL EXCEPTION: main
06-26 17:29:27.171: E/AndroidRuntime(853): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.sai.samples.views/com.sai.samples.views.GalleryView}: java.lang.NullPointerException
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569)
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.os.Handler.dispatchMessage(Handler.java:99)
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.os.Looper.loop(Looper.java:130)
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.app.ActivityThread.main(ActivityThread.java:3683)
06-26 17:29:27.171: E/AndroidRuntime(853):  at java.lang.reflect.Method.invokeNative(Native Method)
06-26 17:29:27.171: E/AndroidRuntime(853):  at java.lang.reflect.Method.invoke(Method.java:507)
06-26 17:29:27.171: E/AndroidRuntime(853):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
06-26 17:29:27.171: E/AndroidRuntime(853):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
06-26 17:29:27.171: E/AndroidRuntime(853):  at dalvik.system.NativeStart.main(Native Method)
06-26 17:29:27.171: E/AndroidRuntime(853): Caused by: java.lang.NullPointerException
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:100)
06-26 17:29:27.171: E/AndroidRuntime(853):  at com.sai.samples.views.GalleryView.<init>(GalleryView.java:24)
06-26 17:29:27.171: E/AndroidRuntime(853):  at java.lang.Class.newInstanceImpl(Native Method)
06-26 17:29:27.171: E/AndroidRuntime(853):  at java.lang.Class.newInstance(Class.java:1409)
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
06-26 17:29:27.171: E/AndroidRuntime(853):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1561)
06-26 17:29:27.171: E/AndroidRuntime(853):  ... 11 more

任何帮助都将受到高度赞赏。

Answer 1

应在getApplicationContext()内调用

onCreate()。我不认为在创建活动之前调用它是有效的。

Answer 2

此行导致 NPE

ga.setAdapter(new ImageAdapter(context));

因为您的上下文是null，所以当您在活动的onCreate()

之外进行初始化时

实际上，

这些是您的死代码，（您无法在活动方法的外部获取应用程序上下文或不参考它）

public Context context=getApplicationContext();
Bitmap icon1 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica1);
Drawable d1 =new BitmapDrawable(context.getResources(),icon1);
Bitmap icon2 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica2);
Drawable d2 =new BitmapDrawable(context.getResources(),icon2);
Bitmap icon3 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica3);
Drawable d3 =new BitmapDrawable(context.getResources(),icon3);
Bitmap icon4 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica4);
Drawable d4 =new BitmapDrawable(context.getResources(),icon4);
Bitmap icon5 = BitmapFactory.decodeResource(context.getResources(),
        R.drawable.antartica5);
Drawable d5 =new BitmapDrawable(context.getResources(),icon5);

您不能在onCreate（）或任何其他Activity方法的外部执行此操作。

所以把这些代码放在onCreate（）方法的活动中。

像，

public Context context;
Bitmap icon1, icon2, icon3, icon4, icon5;
Drawable d1, d2, d3, d4, d5; 
public Map< Integer,Drawable> dayMap;
ImageView imageView;


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main_gallery);
 context=getApplicationContext();
 icon1 = BitmapFactory.decodeResource(context.getResources(),
            R.drawable.antartica1);
 d1 =new BitmapDrawable(context.getResources(),icon1);
 icon2 = BitmapFactory.decodeResource(context.getResources(),
            R.drawable.antartica2);
 d2 =new BitmapDrawable(context.getResources(),icon2);
 icon3 = BitmapFactory.decodeResource(context.getResources(),
            R.drawable.antartica3);
 d3 =new BitmapDrawable(context.getResources(),icon3);
 icon4 = BitmapFactory.decodeResource(context.getResources(),
            R.drawable.antartica4);
 d4 =new BitmapDrawable(context.getResources(),icon4);
 icon5 = BitmapFactory.decodeResource(context.getResources(),
            R.drawable.antartica5);
 d5 =new BitmapDrawable(context.getResources(),icon5);
 .
 .
 .

如何从位图图像创建图库？

2 个答案: